Population Genetics and Phylogeography of Two Large-River Freshwater Mussel Species at Large and Small Spatial Scales

by Monroe, Emy M.

Abstract (Summary)

Species distributions and population genetic structure are determined by landscape history and biological characteristics of an organism. Pleistocene glaciations affected species distributions and freshwater drainage patterns. Extensive work on the biogeography of fish has determined the effects of glaciations on genetic population structure and described recolonization routes from glacial refugia. Freshwater mussels are intimately tied to fish because larvae are largely obligate parasites on fish. Dispersal via hosts has likely led to similar patterns in genetic structure and distributions of mussels and fish. I quantified genetic diversity using mitochondrial DNA and allozymes to determine genetic population structure and infer evolutionary history for Cumberlandia monodonta an endangered species (Chapter 2). There was a lack of genetic structure and evidence of high gene flow. The phylogeny indicated isolation in two glacial refugia followed by post-Pleistocene dispersal of two lineages range-wide. The distribution of Lampsilis cardium, a non-endangered species, spans glaciated and non-glaciated areas. Genetic diversity was quantified in northern and southern populations to determine if this large-river species has similar patterns found in other species of fish and mussels (Chapter 3). Genetic data from populations in the upper midwest and Canadian drainages were used to test hypotheses of dispersal from the upper Mississippi River (UMR) into the Red River of the north (RRN). Overall genetic diversity was high, but populations in the north and south had similar levels. There was evidence for two glacial refugia in the Great Lakes basin, but not the upper midwest. Genetic data did not support the hypothesis of post-Pleistocene dispersal from the UMR into the RRN. On a smaller spatial scale, genetic variation and structure of L. cardium from the UMR was also quantified with microsatellite markers (Chapter 4). The UMR is fragmented with locks and dams creating distinct river reaches, therefore, population genetic variation and structure were measured within a spatial hierarchy. Historic and contemporary gene flow were compared to determine if the dams are affecting genetic diversity. Genetic diversity was high, and populations in the UMR may be panmictic. There is evidence that fragmentation may be reducing gene flow for this species.